Semiconductor components, for example photodiodes or phototransistors, can be used for detecting light. What is common to these components is that they have a pn junction around which a space charge zone forms which can be enlarged by means of a correspondingly applied external voltage. Light absorbed by the semiconductor body generates charge carriers pairs which are separated in the electric field of the space charge zone and forwarded to corresponding external contacts.
Silicon, for example, can be used as semiconductor material for light-sensitive semiconductor components, particularly if the components are integrated with integrated circuits. However, the absorption spectrum of silicon has an increasing absorption toward shorter-wave light. The consequence of this is that incident light in the range up to a wavelength of approximately 460 nm has only a small penetration depth into the silicon. This has the effect that said light is already almost completely absorbed in the semiconductor in a depth of approximately 80 nm. For the detection of such short-wave light, therefore, the semiconductor is only available up to this penetration depth.
What is disadvantageous about this fact is that known light-sensitive semiconductor components usually have a vertically oriented semiconductor junction and have a highly doped layer as topmost layer in order to realize the semiconductor junction. In this highly doped layer near the surface, however, charge carrier separation can only be effected with a reduced yield since, as a result of the high charge carrier concentration, the lifetime of the minority charge carriers is short and, on the other hand, the electric field of the space charge zone cannot extend over the entire highly doped layer, with the result that minority charge carriers generated there can pass to the corresponding current-delivering contact only by means of diffusion. However, this process is slow, increases the decay time of the photocurrent, and additionally increases the probability that charge carrier pairs will recombine and can therefore no longer contribute to the signal current of the component.
In order to increase the blue sensitivity of light-sensitive semiconductor components composed of silicon, various approaches have already been pursued. U.S. Pat. No. 4,107,722 A proposes producing, in a semiconductor body in a zone of the first conductivity type, a highly doped thin layer near the surface of the same conductivity type but with a different dopant. Alongside the actual semiconductor junction with a zone of the second conductivity type, a second semiconductor junction is produced in this way and generates a weak internal electric field that can additionally accelerate the charge carriers. However, said field is significantly smaller than the field that is formed in the space charge zone or applied externally to the space charge zone. Therefore, the charge separation speed is an order of magnitude lower than within the space charge zone. The consequence of this is that the component reacts to the incidence of light only sluggishly or requires a long decay phase until the last charge carrier pairs can be conducted away at the contacts.
U.S. Pat. No. 4,968,634 A discloses firstly producing a shallow doping in the surface of a semiconductor body and then etching the latter back as far as the location of the highest charge carrier concentration. This reduces the layer thickness of the highly doped layer and reduces the proportion of charge carrier pairs generated in said layer.
What is common to most of the approaches for increasing the blue sensitivity of semiconductor components is that they either have a reduced light sensitivity and/or require a long decay time, which make the components slow. Such components are not suitable for the sensitive detection of light pulses with high pulse rates.